Artificial vessel prostheses for replacing blood vessels and other hollow organs of the human or animal body are known. Thus, there are knitted vessel prostheses, cf. DE-A-24 61 370, U.S. Pat. No. 3,945,052 and U.S. Pat. No. 4,047,252, as well as woven prostheses, cf. EP-B1-108 171. The prostheses can have a smooth surface and can be in the form of a single or double velour, as is apparent from the above documents. In addition, the prostheses can have a so-called bifurcation, i.e. a forking into generally two thinner branches. The known prostheses comprise cylindrical tubular portions with a constant diameter, apart from a diameter reduction as a result of the bifurcation. The prostheses can also be corrugated or ribbed, which is generally referred to in the art as pleating. The prostheses can be impregnated with a resorbable or non-resorbable sealing medium for the sealing of the textile wall structure. They can also be used in the unimpregnated state and during the operation there is at least a precoagulation of the prosthesis wall with the blood of the patient, in order to bring about the necessary sealing until the weave has grown into the wall structure.
In order to obtain favourable flow conditions, vessel prostheses can be given a conical configuration in much the same way as natural blood vessels. Such a conical vessel prosthesis of non-textile material and the production thereof is described in EP-A2-391 586. For the production thereof a polytetrafluoroethylene, extruded tubular fabric is initially stretched to 2 to 6 times its original length and becomes porous. This is followed by an expansion of the porous tubular fabric by an expanding engaging or pushing onto a conical mandrel, which is ultrasonically excited. A similar non-textile, conical vessel prosthesis is described in East German patent 160857. Textile vessel prostheses with a stepped diameter are also commercially available, without details of their manufacturing procedure being known. Such prostheses are also incorrectly called conical. DE-OS 22 55 743 discloses a textile vessel prosthesis with different diameters at its ends and which is conically constructed in the longitudinal direction. The vessel prosthesis is produced by generally known knitting methods. In particular, it is produced on a fine pitch flat knitting machine with a number of needles corresponding to the required inside width or diameter. The stitches or loops are successively removed and placed in inactive needles, so that at the end the inside width corresponds to the requisite inside width of the prosthesis.
Another textile vessel prosthesis with diameter variation is known from the publication PLANCK, HEINRICH: Development of a textile arterial prosthesis with fibrous structure (in German), Stuttgart University thesis, 1980, p 38. The diameter variation is brought about in that with the aid of additional binding threads the free inside diameter of the knitted tubular prosthesis is adjusted and conical prostheses can be produced using the same procedure.